i had a 307 in my 70 nova also. what i did was i got a set of vortec heads. mine came off of a 97 tahoe. i used a compcams 270h hyd. flat tappet cam. it gives it a nice little rumble. for my intake i got a summit stage one duel plane intake. and a edelbrock 650 carb. hei ignition. i was surprised how much that thing pulled. i did that because the bottom end was still good. but if you have to rebuild it put the money in a 350.